1. Field of the Invention
The present invention relates to a hot melt ink-thermal transfer recording material for recording hot melt ink images by a thermal transfer recording system. More particularly, the present invention relates to a hot melt ink-thermal transfer recording material having an enhanced ink-receiving property and a satisfactory applicability to offset printing and being capable of recording clear ink images with a high durability and thus useful for recording thereon bar codes.
2. Description of the Related Art
Currently, bar code recording systems are utilized in various fields, for example, merchandise control in department stores and supermarkets, load control in forwarding agents and attendance control in enterprises and offices.
Especially, for the bar code records used in industry, high reliability and durability (persistency) in storage of the record are required.
Recently, for the bar code recording system, various printing methods, for example, the electrophotographic printing method, thermal transfer printing method, and ink-jet printing method have been employed. These printing methods have both merits and demerits.
Namely, among these printing methods, the ink-jet printing method is disadvantageous in that the recorded ink images have a poor resistance to water and fade significantly on exposure to ultraviolet rays. The electrophotographic printing method is disadvantageous in that when the recorded images are brought into contact with a plastic film, for example, a polyvinylidene chloride film, a toner contained in the recorded images is easily dissolved in a plasticizer contained in the plastic film. Accordingly, currently, the hot melt ink-thermal transfer recording method which can record clear images having a higher persistency and durability than those produced by the electrophotographic printing method and the ink-jet printing method has generated strong interest as a bar code recording method. This method is advantageous in that ordinary paper sheets can be used as a recording medium.
The thermal transfer printing method is, however, still unsatisfactory in water resistance, abrasion resistance and difficulty of alteration and thus, its performance should be improved in these categories. Some attempts have been made to reduce these drawbacks by changing the composition of the ink used. However, these attempts have not yet been satisfactory. Therefore, there is strong demand for an improvement of the recording material or medium.
The conventional bar code-recorded material is unsatisfactory, for example, in that when the bar code images are immersed in water for several hours, the ink is separated from the recording material and floats on water, or the ink images are easily removed from the recording material when rubbed with a cosmetic liquid, for example, hair tonic. These disadvantages of the thermal transfer printing method can be removed only by improving the performance of the ink image-receiving material.
Also, due to an increase in bar code treatment speed, the recording material is strongly required to exhibit high speed recordability, an enhanced brightness of the recorded images and a high resolving power. If a conventional paper sheet is used as a recording sheet for a high speed ink thermal transfer printing method, the resultant prints are uneven in ink image quality and have defects of dots due to poor surface smoothness and a low ink-receiving property of the paper sheet.
To improve the surface smoothness of the recording paper sheet, some attempts have been made to control the Bekk smoothness of the paper sheet or to provide a specific thermal transfer ink-receiving layer containing a specific pigment or binder resins. These attempts had a certain improving effect for the surface smoothness. However, the attempts were not completely successful because they resulted in a decrease of the distinctness of the recorded ink images, due to defectively dotted ink images and poor reproducibility of the dotted ink images.
Accordingly, it is recognized that the disadvantages of the conventional ink thermal transfer recording materials cannot be completely removed only by enhancing the surface smoothness thereof or adding a specific pigment or binder resin to the ink-receiving layer. Namely, a hot melt ink type thermal transfer recording material having a high persistency or durability and distinctness of the recorded images, an enhanced ink-receiving property and an excellent reproducibility of dotted ink images has not yet been obtained.
In the conventional thermal transfer recording sheet, it is necessary to use a binder in a very small amount for the ink-receiving layer to enhance the hot melt ink-absorption thereof. Therefore, the resultant ink-receiving layer exhibits a poor surface strength to the printing ink and thus is not suitable for offset printing.